[caldav] Sync calendars even if they have not been previously synced for an account

Since an account has multiple calendars, the decision to choose a slow
sync versus a quick sync for a notebook should depend on whether a
notebook already exists for a particular calendar, rather than whether
the account has previously been synced.
Merge pull request #14 from nemomobile/sync-new-calendars

[caldav] Sync calendars even if they have not been previously synced for...